Clustered discrete Fourier transform-spread orthogonal frequency-division multiplexing (hereinafter represented as clustered DFT-S-OFDM for short) has been accepted as an uplink multiple access solution for LTE-Advanced. In clustered DFT-S-OFDM, the output of a DFT block is divided into a few clusters and each cluster of data is separately mapped to a sub-band. This discontinuous radio band allocation makes clustered DFT-S-OFDM distinguished from SC-FDMA (Single Carrier—Frequency Division Multiple Access). Although this feature provides more frequency diversity gain, it has the disadvantage of increasing the PAPR (Peak-to-Average Power Ratio).
FIG. 1 illustrates the structure of a prior art transmitter employing clustered DFT-S-OFDM. As shown in FIG. 1, after the date is Turbo coded, modulated, and 2M-point discrete Fourier transformed, the output of the DFT block is divided into two clusters. The two clusters of data blocks are mapped to sub-band 1 and sub-band 2 respectively, and are finally transmitted via an antenna. The transmitter solution shown in FIG. 1 is called prior art solution 1 hereinafter. As described above, the disadvantage of the solution lies in its high PAPR.
There has been proposed a grouping method used in DFT-S-OFDM. In this method, two clustered of modulated data are allocated to two antennas and each cluster of data is transmitted via one of the antennas, thereby mitigating the PAPR. FIG. 2 illustrates the structure of a transmitter according to this method. As shown in FIG. 2, the data is divided into two clusters after being Turbo coded and modulated, and the two clusters of data are discrete Fourier transformed separately. The first cluster of data is mapped to sub-band 1 and transmitted via antenna 1, while the second cluster of data is mapped to sub-band 2 and transmitted via antenna 2. In this method, each transmit antenna corresponds to a cluster of data, thereby mitigating the PAPR. However, a portion of frequency diversity gain is lost. The transmitter solution shown in FIG. 2 is called prior art solution 2 hereinafter.